This invention relates generally to a labeling apparatus and method for applying labels to containers, and more particularly to a labeling apparatus and method employing a radiation curable adhesive for adhering a label to a container. The labels employable in this invention are in the form of plastic, sheet fed/cut and stack labels, and can be formed of films that are transparent or opaque (including metallized films). Most preferably the radiation curable adhesive is a UV curable adhesive.
A number of prior art systems exist for applying labels to containers. These systems employ either continuous roll fed labels or cut and stack labels.
Prior art labeling apparatus and methods employing labels in continuous roll form include label cutting and registration means for severing discrete labels from the roll and then registering them for attachment to the containers through a vacuum transfer drive system. In these prior art systems a hot melt adhesive generally is employed; being applied to both the leading and trailing edge of the back side of the labels for permitting attachment of the labels to the containers.
Although the above-described system is being commercially utilized, it does include a number of drawbacks for various applications. First, continuous roll fed labeling systems require both label cutting and registration units, which increase the complexity of the system. Second, hot melt adhesives are, at best, generally cloudy or milky in appearance and therefore are not effectively utilized to apply clear or transparent labels in a uniform fashion to clear containers. The uniform attachment of clear or transparent labels to clear containers, e.g., clear glass or plastic beer and soda bottles, is very desirable, providing a very clean finish, and also permitting the product inside of the bottle to be clearly and easily viewed through the label. A further deficiency in connection with the use of hot melt adhesives is that they generally are difficult to apply as a smooth, continuous layer to the label stock.
It is known to employ continuous rolls of transparent pressure sensitive labels for application to clear containers. However, as discussed above, the use of these continuous rolls require cutting and registration units that increase the complexity of the system. Moreover, the rolls of pressure sensitive labels often include a release liner covering the adhesive surface, thereby necessitating the removal of the release liner from the label during the continuous process. This also introduces an undesired complexity and cost into the system.
It also is known to apply sheet fed/cut and stack labels (i.e., labels that have been cut off line and are retained in a stack within a dispensing magazine) to containers, such as bottles, in a continuous label application system. These latter prior art systems often employ a cold glue adhesive, which is water soluble, and sometimes employ a hot melt adhesive. When a cold glue adhesive is employed it is applied to a glue transfer pad by a transfer roll that commonly is made of steel, and then the glue transfer pad is moved into contact with the lower label of the stack to both apply the glue to that label and remove the label from the stack through surface adhesion between the label and the adhesive. Thereafter, the label, with the cold glue adhesive thereon, is moved to a transfer drum, from where it is then applied to a container, such as a glass bottle. These cold glue adhesives generally have been utilized only in connection with paper labels that are capable of absorbing the moisture from the water soluble adhesives. In other words, systems employing water soluble cold glue adhesives are not well suited for use with non-porous, plastic labels. Although hot melt adhesives also have been employed with cut and stack labels, they are subject to the same deficiencies discussed above with respect to the use of such adhesives on continuous label stock.
Based on the deficiencies of the existing prior art systems, a need exists for a labeling apparatus and method that is not required to handle an excessively tacky adhesive throughout the label handling and applying operations, and that is effective for use with plastic labels for adhering such labels to containers. Although the desired systems of this invention are usable with both opaque and clear plastic labels to adhere such plastic labels to both opaque and clear containers, the most significant need exists in providing a system for adhering clear plastic labels to clear containers, such as clear glass bottles, e.g., beer or soda bottles, without the presence of unsightly striations or other unsightly imperfections in the adhesive distribution.
Most preferably a need exists for the aforementioned type of system that does not require the use of label cutting and registration units of the type generally employed in labeling apparatus and methods that handle continuous roll fed labels.
It is a general object of this invention to provide a method and apparatus for applying plastic labels to containers that are reliable in operation.
It is a further object of this invention to provide a method and apparatus for applying plastic labels devoid of any release liner to containers in a reliable manner.
It is a further object of the most preferred embodiment of this invention to provide a method and apparatus for applying transparent plastic labels to clear containers in a reliable manner.
It is a more specific object of this invention to provide a method and apparatus for applying transparent plastic labels to clear containers without unsightly striations or other unsightly imperfections in the adhesive.
It is a further object of the most preferred embodiment of this invention to provide a sheet fed, cut and stack, labeling method and apparatus for applying plastic labels to containers that do not require the use of label cutting and registration devices of the type included in labeling systems that handle labels in continuous roll form.
It is still a further object of this invention to provide a method and apparatus for applying a plastic label to a container wherein an excessively tacky adhesive is not required to be handled throughout the entire label forming and applying operations.
It is yet a further object of this invention to provide a method and apparatus for applying a plastic label to a container wherein an adhesive is rendered sufficiently tacky to effectively adhere it to the container just prior to applying the label to the container; the result being equivalent to utilizing a conventional pressure-sensitive label but without the attendant drawbacks thereof, as discussed earlier.
The above and other objects of this invention are achieved in a labeling apparatus and method wherein a radiation curable adhesive, which is not excessively tacky prior to curing (or partial curing), is applied to the surface of a label to be attached to a bottle, and the label, with the radiation curable adhesive thereon, is then sequentially fed through a curing operation to render the adhesive sufficiently tacky to adhere the label to a container, and then to a station for immediately applying the label to a surface of the container through the tacky adhesive on the label.
It is within the scope of this invention to cure the adhesive to a full pressure sensitive state in the curing operation. In this condition, additional curing of the adhesive after the label is applied to the container is not required to take place, and in fact, does not take place; the adhesive being sufficiently tacky to assure that the label remains permanently adhered to the container during normal handling of the container. It also is within the scope of this invention to only partially cure the adhesive in the radiation curing step to render the adhesive sufficiently tacky to initially adhere the label to a container. However, thereafter the adhesive will continue to cure, or set-up, to assure that the label remains permanently adhered to the container during normal handling of the container.
In accordance with the most preferred embodiment of this invention, the radiation curable adhesive is curable with ultraviolet radiation, although it is within the scope of the broadest aspects of this invention to employ other types of radiation curable adhesives, such as adhesives curable by radio frequency radiation and electron beam radiation. The most preferred adhesives useable in this invention should have a sufficiently low viscosity to permit them to be applied by an adhesive applicator roll to outer surfaces of transfer pads on a rotating support member for subsequent application from the transfer pads substantially continuously and uniformly to the surface of a label to be adhered to a container. When the label is a cut and stack label, the adhesive also needs to have a sufficient initial tack (hereinafter sometimes referred to as xe2x80x9cminimal tackxe2x80x9d) to permit the transfer pads, with the adhesive on the surface thereof, to remove the lowermost label from a stack of such labels retained within a magazine at the time that the adhesive also is being applied to that label by a transfer pad. This initial, or minimal tack cannot be so strong as to preclude peeling the label from the transfer pad at a subsequent station at which the adhesive on the label is at least partially cured, in a manner to be further explained hereinafter.
In the most preferred embodiments of this invention, particularly when the labels are transparent and are adhered to clear containers, the adhesive is a UV curable adhesive that has the ability to cold flow after application of the label to the bottle to eliminate, or at least minimize the existence of unsightly adhesive striations between the label and container.
Most preferably, when transparent labels are being utilized in the method and apparatus of this invention, the UV curable adhesive is applied with a coat weight of at least 6 pounds per ream and more preferably in the weight range 7 to 8 pounds per ream, or even greater. Preferably this adhesive is applied to the label at a sufficient thickness to enable the adhesive to cold flow after the label is applied to the bottle, and thereby fill in unsightly striations that often are formed in the adhesive between the label and the bottle. An adhesive thickness in the range of about 1 to about 1.5 mils has been determined to cold flow after application of the label to the container, to fill in unsightly striations and other visual defects in the adhesive layer.
In accordance with the most preferred embodiment of this invention, the labels are individual, cut and stack labels retained in a magazine, and a UV curable adhesive is applied to a lower surface of each label in the stack through a rotating transfer pad that moves sequentially through an adhesive application station in which a measured quantity of UV curable adhesive is transferred to the exposed surface of the pad, and then to a transfer station wherein the adhesive on the exposed surface of the pad engages the lowermost label in the stack to both apply the adhesive to that label and remove the label from the stack through the surface adhesion created between the label surface and the xe2x80x9cminimal tackxe2x80x9d of the uncured UV curable adhesive. Reference throughout this application to the adhesive having xe2x80x9cminimal tackxe2x80x9d or being xe2x80x9cminimally tackyxe2x80x9d refers to a tacky condition that is sufficient to engage and remove the lowermost label from a stack of cut and stack labels retained in a magazine, but which is not so strong as to either preclude peeling of the label off of the transfer pad at a subsequent cure station, or to permit the uncured adhesive to consistently, reliably and effectively adhere the label to a container in a commercial labeling system and method. Reference in this application to a label being xe2x80x9ceffectively adheredxe2x80x9d to a container, or to the xe2x80x9ceffective adherencexe2x80x9d of a label to a container, or words of similar import, means that the label is required to be secured to the container in a manner that precludes the edge regions or body thereof from unacceptably separating from the container wall during handling and use of the container, and most preferably, although not required within the broadest scope of this invention, in a manner that prevents an individual from easily peeling the label off of the container.
Therefore, in order to produce commercially acceptable, labeled containers in accordance with this invention the radiation curable adhesive must be at least partially cured prior to the label being applied to the container to assure that the adhesive is rendered sufficiently tacky to achieve the desired effective adherence of the label on the container. In accordance with the preferred embodiment of this invention, the UV curable adhesive may be only partially cured at the time that the label is applied to the container and then, in a relatively short time, become more completely cured to provide effective adherence of the label on the container.
In the most preferred embodiment of this invention the UV curable adhesive is comprised of free radical and/or cationic initiators and monomers that are polymerizable by these mechanisms; and is capable of flowing while curing on a container to fill in imperfections, e.g., striations, in the initial distribution of the adhesive on the label.
In the most preferred embodiment of this invention, the individual labels carried on the transfer pads are then directed to a transfer assembly, wherein the individual labels, with the minimally tacky, UV curable adhesive applied thereto, are released from the pads and directed by the transfer assembly through a UV cure station in which the UV curable adhesive is rendered sufficiently tacky to permit the label to be reliably and effectively adhered to a surface of a container, and then into a label application station for transferring each individual label, with the sufficiently tacky adhesive thereon, to the outer surface of a container, preferably a glass container, such as a beer or soda bottle, to thereby effectively adhere the label to the container.